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ID Category [?] Severity [?] Reproducibility Date Submitted Last Update
07876 Image Enhancement Minor Always Feb 15, 2021, 23:02 May 1, 2023, 16:09
Tester ICEknight View Status Public Platform MAME (Official Binary)
Assigned To Resolution Open OS
Status [?] Acknowledged Driver
Version 0.228 Fixed in Version Build 64-bit
Fixed in Git Commit Github Pull Request #
Summary MESS-specific 07876: genesis and clones: NTSC composite "rainbow effect" inaccuracies with HLSL (bgfx)
Description Trying to get HLSL's NTSC emulation to look like my Genesis Nomad and Japanese Mega Drive's composite output, I noticed that the "rainbow effect" looks more saturated than real hardware and its position seems to be a bit shifted (which might be related to ?).

Best game for testing has to be Zero Tolerance, which shows some (accidental?) "holographic foil" effect on the title screen when using composite NTSC video (the effect isn't visible over RGB or on PAL systems).
Steps To Reproduce -First load zerotol under the Genesis or Mega Drive system, using -video bgfx
-Then, in order to get clean screenshots comparable to what you'd get on real hardware captures, configure HLSL like this:
----Effect: hlsl
----Shadow Mask: white
----Enable NTSC: On
----NTSC A Value: 0.00
----NTSC B Value: 0.00
----Scanline Duration (uSec): 47.7
----Phosphor Persistence, Red: 0.00
----Phosphor Persistence, Green: 0.00
----Phosphor Persistence, Blue: 0.00
----Scanline Amount: 0.00
-Then just wait for a bit for the title screen to show up.
Additional Information I'm including direct video captures with both a generic Scart to HDMI adapter and an OSSC, for reference (all of them adjusted to a correct 4:3 aspect ratio):

NTSC composite:


PAL composite:

Github Commit
Flags Verified with Original
Regression Version
Affected Sets / Systems genesis and clones
Attached Files
png file icon mame 47.7.png (323,829 bytes) Feb 15, 2021, 23:02 Uploaded by ICEknight
MAME HLSL (scanline duration 47.7)
png file icon crop composite generic.png (879,349 bytes) Feb 15, 2021, 23:05 Uploaded by ICEknight
Genesis Nomad, composite, captured with generic Scart to HDMI (cropped)
png file icon composite generic.png (993,588 bytes) Feb 15, 2021, 23:07 Uploaded by ICEknight
Genesis Nomad, composite, captured with generic Scart to HDMI (full)
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May 11, 2021, 22:17
edited on: May 11, 2021, 22:50
Updated links to corrected footage and removed redundant video (sorry for any inconveniences due to the bump).